1. Field of the Invention:
This invention relates to an image reader adapted to read an image and send out the image information to an external machine.
2. Description of the Prior Art:
In these days in which the improved image-processing and image-transmission techniques are available, it is demanded that an independently-usable image reader and an image reader combined with an original feeder to read a large quantity of originals come into existence. There are some problems which possibly arise while an apparatus of this kind is practically used. Namely, when a trouble occurs in an external machine (for example, a host computer, hard copy device or the like) to which the image information is fed, or when an external machine is busy the image information fed out to the external machine is ignored so that an apparent image reading error occurs. A prolonged interruption of an operation of the apparatus causes the alternation of the quantity of light from a lamp to cause an image signal, which is generated after the reading operation is resumed, to be deteriorated.
A problem occurring while such apparatuses are used practically is that the optimum processes (binarization methods or other modified methods) for line and letter originals (which will herein-after be called simply as "line originals") and gradient originals are different. For example, in order to binarize an image signal with respect to a line original it is necessary to use a fixed threshold value corresponding to the density of the ground. In order to binarize an image signal with respect to a pictorial image original (toned image original) it is necessary to use a dither process. If these binarization methods are used inversely, the letters in a line original are broken, so that the reproducibility of thin lines decreases greatly, and the portions of an intermediate tone of color of a pictorial image original are not reproduced properly, i.e. a pictorial image original is reproduced darkly in its entirety. Therefore, the line originals and pictorial image originals must be collected separately in advance to be fed to an image reader. This makes it necessary to carry out troublesome operations for sorting the originals according to their types and arrange the originals in order of page after the reading thereof has been completed. It takes very much time to carry out these operations, and it becomes impossible to make the best use of the functions of an automatic document feeder.